Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $233.91   6.195%   $248.4007   $248.40   $248.40   $248.40  
  Purchase #2 $219.54   8.318%   $237.8013   $237.80   $237.80   $237.80  
  Purchase #3 $99.58   11.489%   $111.0207   $111.02   $111.00   $111.00  
  Purchase #4 $64.73   5.801%   $68.485   $68.49   $68.50   $68.50  
  Purchase #5 $103.86   9.784%   $114.0217   $114.02   $114.00   $114.00  
  Purchase #6 $12.69   6.348%   $13.4956   $13.50   $13.50   $13.50  
  Purchase #7 $215.75   4.130%   $224.6605   $224.66   $224.65   $224.70  
  7 purchase totals = $950.06       $1,017.8855   $1,017.89   $1,017.85   $1,017.90